Final answer:
A ventricular pacemaker functions properly when pacemaker spikes are visible before each QRS complex on ECG monitoring, indicating effective pacing of the ventricles.
Step-by-step explanation:
The nurse can tell that a ventricular pacemaker is functioning properly when pacemaker spikes appear on the ECG monitoring screen before each QRS complex. This indicates that the pacemaker is effectively pacing the ventricles. The purpose of the pacemaker spike is to initiate the depolarization of the ventricles, represented by the QRS complex. In contrast, a pacemaker designed to pace the atria would produce spikes before the P wave, while spikes after the QRS complex or with the T wave would be inappropriate for standard pacing function.